Systematics of BX3 and BX2+ Complexes (X = F, Cl, Br, I) with Neutral Diphosphine and Diarsine Ligands

The coordination chemistry of the neutral diphosphines, R2P(CH2)2PR2 (R = Me or Et) and o-C6H4(PR′2)2 (R′ = Me or Ph), and the diarsine, o-C6H4(AsMe2)2, toward the Lewis acidic BX3 (X = F, Cl, Br, and I) fragments is reported, including several rare complexes incorporating BF3 and BF2+. The studies have revealed that the flexible dimethylene linked diphosphines form [(BX3)2{μ-R2P(CH2)2PR2}] exclusively, confirmed by multinuclear NMR (1H, 11B, 19F{1H}, and 31P{1H}) and IR spectroscopy and microanalytical data. Crystallographic determinations of the four BX3 complexes with Et2P(CH2)2PEt2 confirm the 2:1 stoichiometry and, taken together with the spectroscopic data, reveal that the Lewis acid behavior of the BX3 fragment toward phosphine ligands increases in the order F ≪ Cl ∼ Br < I. The first diphosphine- and diarsine-coordinated dihaloboronium cations, [BX2{o-C6H4(EMe2)2}]+ (E = P, As), are obtained using the rigid, preorganized o-phenylene linkages. These complexes are characterized similarly, and the da...